1. Field of the Invention
The present invention relates generally to an apparatus for producing a thermal stress relieving zone in an automotive heat exchanger. More particularly, the present invention relates to an apparatus for shearing a side support of an automotive heat exchanger core to produce a thermal stress relieving zone.
2. Disclosure Information
Typical automotive heat exchangers, such as radiators, include a plurality of thin-walled tubes interleaved with corrugated fins enclosed in a core frame. The fins are rigidly attached to the tubes as well as to a pair of frame side supports while the tubes are joined to a pair of headers. The frame side supports are attached also to the headers As is well known in the art, coolant passes from one header through the tubing to the other header. As the temperature of the coolant passing through the heat exchanger core increases, the core expands. The frame side supports, however, are not in direct heat contact with the liquid and, as such, do not heat at a proportional rate to the heating of the tubing. As a result of the expansion and contraction of the tubing, the side supports induce thermal stress in the tube-to-header joints during the thermal cycling of the heat exchanger, often leading to durability problems such as cracking or leaking of the tubes.
To overcome this thermal cycling problem and to increase the durability of the heat exchanger core, it is known in the art to relieve the thermally-induced stress by saw cutting the side supports following brazing of the core and prior to placing the heat exchanger core into service. However, the saw cutting operation is difficult to automate, is excessively loud, and produces a tremendous amount of metal fines resulting in increased downtime and increased maintenance of the saw.
Other methods have been proposed to relieve the thermally-induced stress in the heat exchanger core without the need for saw cutting the side supports. For example, U.S. Pat. No. 4,719,967 proposes the use of a "T-shaped" or "I-shaped" slot or piercing stamped into the core reinforcement prior to forming the reinforcement into a channel member. After brazing the core assembly, the reinforcement is fractured at the perforation to allow for expansion of the core during thermal cycling of the heat exchanger. The use of such a "T-shaped" or "I-shaped" perforation may be difficult to maintain since the perforation may fill up with filler metal such as cladding or solder during the brazing of the core and may also prematurely fracture upon bending the reinforcement into its channel shape. Furthermore, U.S. Pat. No. 4,719,967 does not suggest any apparatus for performing the fracturing of the core reinforcement. Therefore, it would be advantageous to provide a simpler and less complex perforation design to avoid these problems.
It is an object of the present invention to provide an apparatus for shearing a side support of a heat exchanger core frame to relieve thermally induced stress experienced by the heat exchanger core.
It is a further object of the present invention to eliminate the saw cutting operation performed on heat exchanger cores and provide a more efficient, cleaner method of providing a thermal stress-relieving zone in an automotive heat exchanger core.
It is an advantage of the present invention to provide an apparatus which automatically receives an automotive heat exchanger from a conveyor assembly and which shears the core side support in an automated procedure.
It is a feature of the present invention that the apparatus produces no fines, chips or slugs and is essentially silent.